1. Field of the Invention
This invention relates to a direct-conversion receiver for a digital-modulation radio signal such as a frequency shift keyed (FSK) signal.
2. Description of the Prior Art
Paging systems of a mobile radio communications network are used for one-way signaling to small receivers (pagers) carried out by individuals. This paging function can signal an individual selectively to take some prearranged action, e.g., call the office, or can deliver a short message. In some of paging systems, a transmitter of a base station can communicate with pagers via digital-modulation radio signals such as frequency shift keyed (FSK) signals.
Direct-conversion receivers can be used as pagers containing FSK demodulators. According to some of the signal transmission standards for a paging system, a base station periodically transmits a digital-modulation radio signal a predetermined number of times, for example, three times. Thus, a pager generally receives a digital-modulation signal the predetermined number of times. The pager selects and uses only one of the first received signal to the last received signal, and disregards the other signals.